This problem isn’t new to the 2010 general election, though the pattern was less neat in 2005. It does raise an interesting question for the party’s get out the vote efforts though, both in terms of technology and targeting.
Some places have made very successful use of technology such as text messaging to remind people to vote, but generally there is very patchy take-up of these sorts of approaches which are likely to be particularly effective with younger voters (more ready to sign up to receive text messages from others, harder to find in when knocking on doors etc.).
Similarly, the use of actual or estimated age data to help identify and then concentrate on younger voters to remind them to vote or to get them sign up to postal votes is more widespread but far from universal.
Learning about and trying out both approaches need not wait until there is an election immediately in the offing, so if your local branch or local party wasn’t already doing both of these to the full, why not make use of the summer months to start a few experiments?